Phenytoin (Epanutin)
Private Phenytoin (Epanutin) testing in London for £73, measuring one therapeutic drug level with results expected in around 1–2 days.
Turnaround time
1-2 business days
Biomarkers count
1
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Overview of the Phenytoin (Epanutin) Test
The Phenytoin blood test measures the concentration of Phenytoin, also known by the brand name Epanutin, in the bloodstream to support therapeutic drug monitoring.
The test assesses 1 specialist drug-monitoring biomarker: Epanutin (Phenytoin).
Phenytoin is an anti-epileptic medicine used to prevent and control selected seizure disorders.
Monitoring is particularly important because Phenytoin has a narrow therapeutic range and unusual pharmacokinetics.
At lower concentrations, relatively small dose changes may produce predictable changes in blood level.
As the enzymes responsible for Phenytoin metabolism become saturated, however, a small increase in dose can sometimes produce a disproportionately large increase in blood concentration.
This makes clinical monitoring important.
Levels that are too low can be associated with inadequate seizure control.
Levels that are too high can cause neurological toxicity.
Common toxicity features include nystagmus, unsteadiness, slurred speech, drowsiness and confusion.
Phenytoin is also highly protein-bound, principally to Albumin.
Low Albumin or severe kidney dysfunction can change the relationship between total Phenytoin and pharmacologically active free Phenytoin.
A total blood concentration therefore needs careful interpretation when Albumin is substantially reduced.
Many medicines interact with Phenytoin because it is metabolised through hepatic enzyme systems and can itself alter the metabolism of other drugs.
Blood-sample timing matters as well.
A trough level collected shortly before the next dose is commonly used when stable therapy is being monitored, although the exact protocol should follow the treating clinician's instructions.
What Does the Phenytoin (Epanutin) Test Check?
The test measures the blood concentration of the anti-epileptic medicine Phenytoin. This test measures 1 specialist biomarker.
Epanutin (Phenytoin)
Measures circulating Phenytoin concentration to support safe dosing, seizure control and assessment of possible drug toxicity.
Who May Benefit From the Phenytoin (Epanutin) Test?
Phenytoin monitoring is useful when treatment effectiveness, adherence, interactions or toxicity needs to be assessed.
People taking Phenytoin for seizure control - Drug-level monitoring can confirm whether exposure is broadly consistent with the intended therapeutic range.
People experiencing breakthrough seizures - A low concentration is one possible explanation.
People with new dizziness, unsteadiness or slurred speech - These can occur with excessive Phenytoin exposure.
People whose Phenytoin dose has recently changed - Repeat measurement can assess the effect of the new dose.
People starting or stopping an interacting medication - Drug interactions can substantially change Phenytoin concentration.
People with significant liver disease - Hepatic metabolism strongly influences Phenytoin.
People with low Albumin or significant kidney disease - Total Phenytoin can become more difficult to interpret.
Pregnant people taking Phenytoin - Pregnancy can alter drug concentrations and requires specialist epilepsy management.
How to Prepare
Do not deliberately skip a Phenytoin dose unless the prescribing clinician has specifically instructed you to do so.
Accurate dose and sample timing are essential for meaningful therapeutic drug monitoring.
Symptoms and Reasons to Consider the Phenytoin (Epanutin) Test
Drug levels are frequently checked according to treatment circumstances rather than symptoms alone.
Breakthrough seizures - Subtherapeutic exposure can contribute to reduced seizure control.
Nystagmus or abnormal eye movements - This is a recognised sign of Phenytoin toxicity.
Unsteadiness or poor coordination - Neurological toxicity can cause ataxia.
Slurred speech - Higher concentrations can impair neurological function.
Confusion or excessive drowsiness - Significant toxicity can affect consciousness and cognition.
Nausea or vomiting with other toxicity symptoms - Gastrointestinal symptoms can accompany high concentrations.
A recent dose or medication change - Repeat testing can determine whether the concentration has shifted.
Severe confusion, inability to walk, reduced consciousness or significant seizure deterioration requires urgent medical assessment.
Do not change or stop Phenytoin suddenly without instructions from the clinician responsible for seizure treatment.
How to Book Your Phenytoin (Epanutin) Test
The Phenytoin test can be booked privately for therapeutic drug monitoring.
Choose the Phenytoin (Epanutin)
Select the individual Phenytoin drug-level blood test online.
Select your sample collection option
Choose an in-clinic blood draw or professional home or hotel phlebotomy able to meet the required sampling time.
Attend your appointment
A trained healthcare professional collects the venous blood sample at the appropriate point in your dosing schedule.
Laboratory analysis
Your serum undergoes measurement of Epanutin (Phenytoin).
Receive your results securely
Your authorised result is delivered securely and should be reviewed alongside dose timing, seizure control, Albumin and clinical symptoms.
When Will I Receive My Results?
The current London Blood Tests page lists a turnaround of approximately 1–2 days after laboratory receipt.
Phenytoin is routinely measured as a therapeutic drug-monitoring assay.
The sample undergoes quantitative analysis, laboratory quality control and result authorisation.
Understanding Your Results
A commonly used total Phenytoin therapeutic range is approximately 10–20 mg/L, although the appropriate concentration must be interpreted clinically.
A low result can indicate insufficient exposure, missed medication, altered absorption or a drug interaction.
Some people remain seizure-free at concentrations below the standard reference interval.
A high result increases concern about toxicity.
Neurological symptoms become particularly important when the concentration is elevated.
Total Phenytoin can be misleading when Albumin is low because a greater proportion of the drug may be unbound and pharmacologically active.
Free Phenytoin measurement or an Albumin-adjusted interpretation can occasionally be required.
Dose adjustment should always be made by the prescribing clinician because Phenytoin concentration can change disproportionately following relatively small dose alterations.
Why Book With London Blood Tests?
London Blood Tests provides private Phenytoin monitoring for people receiving anti-epileptic treatment.
Measures Phenytoin concentration directly - The test provides quantitative therapeutic drug information.
Supports seizure treatment monitoring - Low exposure can contribute to breakthrough seizures.
Helps identify excessive exposure - High levels can produce neurological toxicity.
Useful after dose changes - Repeat measurement can show how the concentration has responded.
Relevant to drug interactions - Many medicines can alter Phenytoin metabolism.
Can be interpreted with Albumin - Protein binding is important when Albumin is low.
Rapid laboratory turnaround - Results are expected approximately 1–2 days after laboratory receipt.
Clear pricing - The Phenytoin (Epanutin) test costs £73.
Private Phenytoin (Epanutin) Blood Test in London
London Blood Tests provides private Phenytoin therapeutic drug monitoring for people receiving Epanutin or another Phenytoin formulation.
The test costs £73 and measures 1 specialist drug-monitoring biomarker.
Results are expected approximately 1–2 days after laboratory receipt.
Dose changes should be made by the treating clinician rather than from the laboratory concentration alone.